The accumulation of dust resulting from electrostatic charging with formation of dust patterns is a widespread problem with moulded plastics articles. Dust deposits on high-gloss moulded articles are particularly troublesome and functionally limiting. A further problem with many moulded plastics articles is the change in intrinsic colour under the influence of ageing processes. More particularly many plastics have a tendency to yellow, for example, under the influence of (UV) light.
The abovementioned problems are often solved by application of an antistatic and light-stable coating (for example by painting). Examples of relevant fields of application include housings applications in information technology and decorative automotive interior components. Especially in the latter field of application a high material ductility even at low temperatures is generally a further component requirement.
If a downstream coating process is to be eschewed the moulding compounds must naturally not only possess the desired mechanical properties but must moreover also possess the required surface properties (high dissipative electrical conductivity/low specific electrical surface resistance and good light stability), However, the desired combination of ductility even at low temperatures, high dissipative electrical conductivity and good light stability is often not sufficiently realized by thermoplastic compositions of the prior art.
Polycarbonate compositions are often employed in the recited fields of application because of their advantageous combination of properties including good processibility (high melt flowability), exceptional mechanical properties, high heat resistance and flame retardancy. However, a technical challenge which has still not yet been resolved adequately for many fields of use of such polycarbonate compositions is still the combined implementation of ductile material characteristics even at low temperatures, good ageing stability, especially adequate lightfastness, and good colourability, as required for many uncoated components. Commercial compositions comprising polybutadiene rubber-based impact modifiers, for example polycarbonate/ABS blends, do have good low-temperature toughness and colourability, but generally have inadequate light stability. Compositions comprising acrylate rubber-based impact modifiers, for example is polycarbonate/ASA blends, by contrast, are light-stable and, in the case of selection of suitable impact modifier types, are sometimes also sufficiently colourable, but have inadequate low-temperature ductility. Compositions comprising silicone rubber- or silicone-acrylate composite rubber-based impact modifiers in turn do have adequate light stability and low-temperature toughness, but have inadequate colouring characteristics. Moreover, although polycarbonate compositions that have been rendered permanently antistatic are basically known, the addition of the additives required for this purpose generally has a disadvantageous effect on the properties desired.
In this respect, another unresolved technical challenge is that of providing polycarbonate compositions that are simultaneously sufficiently permanently antistatic, light-stable, tough at low temperatures and colourable—especially when the application additionally also requires good processibility and processing stability and also high heat resistance, properties that are generally expected from commercial polycarbonate compositions but often cannot be achieved easily.
The literature describes antistats for thermoplastics (see for example Gächter, Müller, Plastic Additives, Hanser Verlag, Munich, 1996, p. 749 ff) which reduce dust accumulation. These antistats reduce the electric surface resistivity of the plastics moulding compounds, resulting in better discharge of surface charges which form during production and through friction during use. Dust particles are thus electrostatically attracted to a lesser extent.
Polyetheramides, polyesteramides or polyetheresteramides are commonly described antistats, and these compounds are capable of rendering polymer compositions permanently antistatic. Their effect is based on the formation of a three-dimensional network of the antistat in the antistat-immiscible polymer to be rendered antistatic. On account of the comparatively high electrical conductivity of polyetheramides, polyesteramides and polyetheresteramides, this results in an instant and permanent reduction in the electrical surface and volume resistivity of the polymer to be rendered antistatic, which sets in even at very low air humidities and is far less dependent thereon than is the case for the surface-active compounds such as salts of long-chain sulphonic acids likewise recited in the literature.
Polycarbonate compositions that have been rendered permanently antistatic are disclosed, for example, in U.S. Pat. No. 6,784,257 B2. This application describes antistatic polymer compositions comprising a thermoplastic polymer and a polyether-polyamide block copolymer having a melting point between 80° C. and 150° C., wherein the polyether blocks comprise ethylene oxide units.
U.S. Pat. No. 6,706,851 B1 discloses antistatic polymer compositions comprising a thermoplastic polymer and a polyetheresteramide block copolymer, wherein the polyether blocks consist essentially of ethylene oxide units.
U.S. Pat. No. 6,913,804 B2 discloses antistatic polymer compositions comprising a thermoplastic polymer and a mixture of a copolymer which comprises polyamide and polyether blocks and does not comprise any ionically functional groups and a copolymer comprising polyamide and polyether blocks which does comprise ionically functional groups.
All three of the abovementioned patents also disclose compositions in which the thermoplastic polymer is polycarbonate, ABS or a mixture thereof.
CN 101967274 A discloses permanently antistatic polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) compositions having excellent mechanical properties and weathering resistance comprising polycarbonate, an ABS resin, antistatic agents, compatibilizers, antioxidants, light stabilizers and other additives. Antistatic agents disclosed include polyetheresters, polyetheresteramides and polyetheramides.
CN 101759974 A discloses antistatic polycarbonate compositions having low odour and high toughness for automotive interior applications comprising polycarbonates, ABS resin produced in a bulk polymerization process and having a melt flow index of 4 to 25 g/10 min, a polymeric antistatic agent, a compatibilizer and optionally further additives selected from for example the group comprising colourants, fillers, stabilizers and lubricants. Antistatic agents disclosed include polyetheramides.
JP 3663701 B2 discloses antistatic polycarbonate compositions comprising polycarbonate, rubber-modified thermoplastic comprising vinyl polymer and graft polymer obtained by grafting vinyl monomers onto rubber-like polymers and polyetheramides.
JP 3611228 B2 discloses antistatic polycarbonate compositions comprising polycarbonate, rubber-modified vinyl/cyanovinyl copolymers, polyetheresteramide block copolymers and metal salt.
WO 2012/084848 A1 discloses antistatic polycarbonate moulding compounds having improved heat resistance, low-temperature toughness, processing stability, stress fracture resistance and hydrolysis resistance comprising polycarbonate, rubber-modified vinyl (co)polymer, a compound selected from the group consisting of polyetheramides, polyesteramides and polyetheresteramides, a specific Brønsted acid and optionally further additives. There is no disclosure of boron salt-containing antistatic agents.
CN 104830043 A discloses antistatic polycarbonate/acrylonitrile-styrene-acrylate (PC/ASA) compositions for decorative automobile interior components, comprising polycarbonate, an ASA resin, impact modifiers, antioxidants, light stabilizers, lubricants, antistatic agents and chain extenders, which feature a reduced tendency to attract dust and well-balanced stiffness and ductility and are light-resistant.
WO 2013/001168 A1 discloses ion-conductive halogen-free polymer blends comprising at least one polyether-based polymer or copolymer selected from the group of the polyether block polymers and polyether-based polyurethanes, characterized in that this blend comprises an alkali metal salt of a boron-centred anionic complex containing bidentate ligands selected from the group consisting of C2-C8 aliphatic or aromatic components having at least two reactive groups selected from —COOH and —OH, where the boron-containing salt in a preferred embodiment is potassium bis(oxalato)borate or sodium bis(oxalato)borate. The application likewise discloses ion-conductive polymer blends also comprising a polymeric material selected from the group consisting of polyamides, polyesters, polyacrylates, polymethylmethacrylates and polyester-based polyurethanes. There is no disclosure of polycarbonate-based blends.
It was desirable to provide permanently antistatic compositions comprising at least one representative selected from the group consisting of aromatic polycarbonate, aromatic polyestercarbonate and aromatic polyester having an improved combination of lowest possible specific electrical surface resistance (sufficiently high dissipative electrical conductivity), excellent colour stability under exposure to heat and light, and low-temperature ductility. The compositions were additionally to have good processibility and processing stability, and also high heat resistance. The compositions were accordingly to fulfil the requirements of the automotive industry for unpainted decorative components in automotive interiors. In addition, the moulding compounds were to have good colourability and, in the coloured state, were to meet the Volkswagen specifications according to PV3977 on dissipative electrical conductivity (experience shows that this requires a specific surface resistance of not more than 1·1012Ω) and according to PV1303 on resistance to heat and light, and have substantially ductile characteristics at −30° C. both in the multiaxial puncture experiment and in the notched impact experiment. In the heat-and-light ageing according to PV1303, the target is a greyscale assessment relative to the starting state prior to exposure of not less than 4 for an exposure period of 3 exposure cycles, preferably even for an exposure period of up to 6 exposure cycles.